Offshore Platform drainage 1

[techv]

Dear members,

We are designing a offshore platform and have come across a basic question on design of hazardous open drainage. There are limitations in treating that and owner decided to collect the contents and ship to onshore. Having decided that they wanted to size the collection tank as small as possible which is possible only by avoiding rain water falling on the collection areas. Since bunds (coaming) is provided under all hydrocarbon vessels the total drainage load has been estimated to be vety high.

In order to overcome the above, Owner raised a query why the pressure vessels (Flare KO Drum, Methanol Drum etc.)need bunds below them. Their point is that since all such pressurised vessels are provided with closed connection to the closed drainage, spillage is not expected from them and hence bunding not required. They are OK with providing bunding for atmoshperic tanks such as diesel and lube oil tanks to cater to overflows etc.

I referred to Shell DEP also but it does not give any clarification which equipment call for bunding and whether Owner's point is right (removing bunds for pressurized vessels). Advise/feedback from you is highly appreciated.

Thanks
Techv

 

[MortenA]

If the "owner" is Shell - then pointing at the DEP should be enough

Best regards

Morten

 

[bimr]

If the tanks are holding any type of oil product, then the facility will be required to have an Oil Spill Prevention, Control, and Countermeasure (SPCC) Plan to prevent releases of oil to the water. The provisions of that plan will require secondary contaminant to prevent an oil spill.

The Spill Prevention, Control, and Countermeasure (SPCC) rule includes requirements for oil spill prevention, preparedness, and response to prevent oil discharges to navigable waters and adjoining shorelines. The rule requires specific facilities to prepare, amend, and implement SPCC Plans.

http://www.epa.gov/emergencies/content/spcc/index.htm

"(c) Provide appropriate containment and/or diversionary structures or equipment to prevent a discharge as described in §112.1(b), except as provided in paragraph (k) of this section for qualified oil-filled operational equipment. The entire containment system, including walls and floor, must be capable of containing oil and must be constructed so that any discharge from a primary containment system, such as a tank or pipe, will not escape the containment system before cleanup occurs. At a minimum, you must use one of the following prevention systems or its equivalent:

.......................
(2) For offshore facilities:

(i) Curbing or drip pans; or

(ii) Sumps and collection systems."

http://ecfr.gpoaccess.gov/cgi/t/tex...ode=40:21.0.1.1.7&idno=40#40:21.0.1.1.7.1.6.7

 

[MortenA]

outside the US nobody have to follow epa rule - uless they feel like it. Other local rules may apply.

Best regards

Morten

 

[BillBirch]

Be careful with the difference between hazardous open and closed drains. Your pressururised vessels would normally be positively isolated from the closed drain system with spec blinds etc, and in the event that such vessels are to be drained in a controlled manner, the blinds would be swung to introduce the contents into that system. On the other hand,any spillage from breaking those flanges would be contained by your coamings and diverted to the open drain system, rather than through grating into the sea. It is surprising how large a slick only a few litres of all will create.

Usual practice is to dump drain systems into open bottomed caisson(s) where hydrogens and water settle out and the oil is skimmed off the top and pumped back into production. If you have your open drain system discharging into the same caisson as the closed drain system, make sure that the drain leg of the former is suffiently lower than the laatter to ensure that pressure discharges due to the closed drain will not introduce vapour through-out the open drain system.